1. Field of the Invention
The present invention relates to a mobile unit having a dial lock function and a method for enabling the dial lock in the mobile unit.
In an effort to prevent stolen mobile units, including portable telephones and automobile telephones, from being used illegally, it is known that a password can be used to enable the dial lock. Once the dial lock is enabled, calling is enabled only when an inputted password agrees with the registered password. It is required to enable the dial lock reliably and safely.
2. Description of the Related Art
Normally, when a mobile unit is delivered by a communication company to a user, if the user wants to enable a dial lock function, a password declared by the user is written as a dial lock password in a programmable read-only memory (PROM) in the mobile unit by means of a ROM writer. A personal identification (ID) number for verification, used to connect with a mobile communication network, must also be assigned to the mobile unit. The personal ID number is also written by the ROM writer.
A password for enabling a dial lock is usually composed of four numerical characters. The password is written in a PROM in a mobile unit by means of a ROM writer. For calling, when the password is entered, dial lock is unlocked. Calling is then enabled. Any person who does not know the password cannot use the mobile unit. That is to say, the legal user of a mobile unit will not be charged for illegal use of the mobile unit.
The personal ID number for verification to be set in a mobile unit is unique. The personal ID number for verification can therefore be predetermined by a communication company or a manufacturer and need not be designated by a distributor dealing in mobile unit. However, the password is determined by the user who wants to enable the dial lock and is declared to a distributor. In this case, if all distributors were equipped with a ROM writer, to write or modify personal ID numbers, there would be no problem. In reality, however, a ROM writer is installed only at reliable strategic distributors' offices.
A user who wants to enable a dial lock declares the password to a distributor. The distributor transports the mobile unit to an office equipped with a ROM writer for writing passwords and asks the office staff to write the password in memory. The mobile unit is returned to the distributor and then handed to the user who has been asked to come the office. In other words, a user who wants to enable a dial lock cannot use his mobile unit while it is at the distributor's office. Moreover, since the password is declared to the distributor, the password may be stolen.